The present disclosure relates to subject matter contained in Japanese Patent Application No. Hei-11-176694 filed on Jun. 23, 1999, which is expressly incorporated herein by reference in its entirety.
1. Field of the invention
The present invention relates to a viewfinder for a camera with an adjustable diopter.
2. Description of the Related Art
There have been proposed various types of viewfinders for use in film cameras, so-called CCD (charge coupled device) still cameras and video cameras. Such viewfinders include an eyepiece lens having its optical axis extending parallel to the optical axis of the taking lens of the camera. The camera operator can view the scene as it is being taken through the taking lens. For convenience to possible users who are subject to myopia or hyperopia, some viewfinders have an adjustable diopter to compensate for the differences in each camera operator""s vision.
A typical viewfinder with an adjustable diopter has an eyepiece lens which is capable of displacement along its optical axis. By displacing the eyepiece lens along its optical axis, the optical distance (i.e., the distance along the optical path) between the eyepiece lens and an object image, which may be formed for example on a focusing screen, is changed so that adjustment in diopter of the viewfinder may be achieved.
The use of this diopter adjustment technique, however, often adds to the dimension of the camera in the direction of displacement of the eyepiece lens, which is inconvenient to many cameras, and in particular, to compact cameras, in which portability is one of the most important factors. Further, the use of the above technique may also result in the camera with its viewfinder protruded from its body, which is also inconvenient to compact cameras.
In view of the foregoing, it is an object of the present invention to provide a viewfinder for a camera with an adjustable diopter, which may be compact in construction and thus highly convenient for use in various cameras, and in particular, in compact cameras.
In accordance with an aspect of the present invention, there is provided a viewfinder for a camera with an adjustable diopter, the camera having a body frame and a taking lens, the taking lens having an optical axis which defines a longitudinal axis of the camera.
The viewfinder comprises: an objective lens mounted on the body frame and having an optical axis extending parallel to the longitudinal axis; an eyepiece lens mounted on the body frame and having an optical axis extending parallel to the longitudinal axis; a focusing screen mounted on the body frame and having a surface on which an object image is formed through the objective lens; and a light-rays-directing optical system mounted on the body frame, for causing light rays from the object image to be directed in a first direction parallel to a predefined transverse axis extending transversely with respect to the longitudinal axis.
The viewfinder further comprises: a first reflective optical element for receiving light rays from the object image and reflecting and directing the received light rays in a second direction opposite to the first direction parallel to the transverse axis; a first mechanism for supporting and guiding the first reflective optical element for linear displacement relative to the body frame and along the transverse axis; a second reflective optical element mounted on the body frame for receiving light rays from the first reflective optical element and reflecting and directing the received light rays in a direction parallel to the longitudinal axis and toward the eyepiece lens; a control knob provided for operation by a camera operator; and a second mechanism for responding to operation of the control knob by causing linear displacement of the first reflective optical element along the transverse axis so as to change optical distance between the focusing screen and the eyepiece lens to achieve adjustment in diopter of the viewfinder.
The control knob may be preferably supported for linear displacement. In such a case, the second mechanism may preferably comprise a mechanism for converting linear displacements of the control knob into linear displacements of the first reflective optical element while providing demagnification of displacement between them. Also, in such a case, the second mechanism may preferably comprise: a two-arm lever mounted on the body frame for pivotal movement and having first and second arms in engagement with the control knob and the first reflective optical element, respectively; and a spring normally urging the first reflective optical element so as to maintain engagement between the first arm and the control knob and engagement between the second arm and the first reflective optical element without any backlash in each engagement.
The control knob may have a knob body and a pin extending from the knob body. In such a case, the first arm of the two-arm lever may have a side edge, wherein the side edge is in engagement with the pin, wherein the side edge is shaped such that the pin and the side edge together form a cam mechanism for converting linear displacements of the control knob into pivotal movements of the two-arm lever.
The body frame may have an eyepiece window, which the eyepiece lens is received in and secured to. In such a case, the control knob may be mounted on the body frame at a position near the eyepiece window.
In a particularly advantageous embodiment, the body frame may include an optical element holder having a recess for receiving and holding the first reflective optical element, and the first mechanism may be provided on the optical element holder so that the first reflective optical element is supported and guided by the optical element holder. In such a case, the control knob may be supported for linear displacement. Further, the second mechanism may comprise: a two-arm lever mounted on the optical element holder for pivotal movement and having first and second arms in engagement with the control knob and the first reflective optical element, respectively; and a spring mounted on the optical element holder and normally urging the first reflective optical element so as to maintain engagement between the first arm and the control knob and engagement between the second arm and the first reflective optical element without any backlash in each engagement.
In accordance with another aspect of the present invention, there is provided a diopter adjustment mechanism for use in a viewfinder of a camera, wherein the viewfinder comprises a plurality of optical elements including a movable optical element, wherein adjustment in diopter of the viewfinder is achieved by linear displacement of the movable optical element along a predefined axis.
The diopter adjustment mechanism comprises: an optical element holder having a recess for receiving and holding the movable optical element; a first mechanism provided on the optical element holder, for supporting and guiding the movable optical element for linear displacement along the axis; a control knob provided for operation by a camera operator; and a second mechanism for responding to operation of the control knob by causing linear displacement of the movable optical element along the axis so as to achieve adjustment in diopter of the viewfinder.
The control knob may be preferably supported for linear displacement. In such a case, the second mechanism may comprise a mechanism for converting linear displacements of the control knob into linear displacements of the movable optical element while providing demagnification of displacement between them. Also, in such a case, the second mechanism may comprises: a two-arm lever mounted on the optical element holder for pivotal movement and having first and second arms in engagement with the control knob and the movable optical element, respectively; and a spring mounted on the optical element holder and normally urging the movable optical element so as to maintain engagement between the first arm and the control knob and engagement between the second arm and the movable optical element without any backlash in each engagement.
The control knob may have a knob body and a pin extending from the knob body. In such a case, the first arm of the two-arm lever may have a side edge, wherein the side edge is in engagement with the pin, wherein the side edge is shaped such that the pin and the side edge together form a cam mechanism for converting linear displacements of the control knob into pivotal movements of the two-arm lever.
In an embodiment, the optical element holder has a pair of trunnions. The two-arm lever has a pair of holes formed therein, for receiving the trunnions. Further, the spring is a helical torsion spring having a coiled portion fitted over one of the trunnions. In addition, the movable optical element may comprise a triangular prism serving as a reflective optical element.